sql.py: run_query(): MissingCastException parsing: Support multiple-word types

sql.py: put_table(): Handle MissingCastExceptions by attempting to call a function with the name of the type on the column

sql_gen.py: Added Functions section with Function and FunctionCall

sql.py: Added MissingCastException and parse it in run_query()

schemas/vegbien.sql: Added cast functions for enum types which map invalid values to NULL

sql.py: put_table(): Fixed bug where some exceptions with no handler would not even allow insertion of no rows into the out_table (due to type mismatch issues), by creating an empty pkeys table as a special case

sql.py: put_table(): Preparing to insert new rows: Fixed bug where main_select needed to be generated after distinct_on was set in the if statement

sql.py: put_table(): log_exc(): Fixed bug where the exception strings rather than the exceptions themselves needed to be put in the set, because exceptions are not comparable with ==

sql.py: put_table(): Moved mk_main_select() call out of try block since it is not related to the exceptions that may be thrown

sql.py: put_table(): log_exc(): Check if exception already caught before to avoid infinite loops